Logic Pro X supports two types of realtime bouncing — one and two cycle.

In lossy audio and video compression, two pass encoding is often used to maximize quality while minimizing file size. In Logic Pro X, two pass bouncing does not affect sound quality at all.

So what is two cycle bouncing used for?

In certain situations, you may want to hear a region’s FX tail at the start of the bounce. In a one cycle pass, the FX tail will not be recorded because the bounce will have already finished. By recording the final bounce at the start of the second pass, the first pass’ FX tail will also be included.